Excel 2003

The worksheet has two columns only, all text.
I'd like to sort the entire worksheet by column A, alphabetically.
Many of my column A entries have multiple related entries in col. B;
that is, cell A2 has related items in B2, B3, B4. A2, A3, A4 are
blank.
A5 has related items in B5, B6, B7, B8, B9 (the A's are blank)
How do I sort by col. A and retain the association of all of the
related col. B items? So that, if the sort moves A5 up to A1, it also
moves B5, B6, B7, B8, B9 up to A1, A2, etc.?

Thanks,

Mike